It is known to inflate an inflatable vehicle occupant protection device to help protect a vehicle occupant upon the occurrence of an event such as a vehicle collision or rollover. One particular type of inflatable vehicle occupant protection device is an inflatable driver or passenger air bag that is inflatable between the occupant and an instrument panel and/or steering wheel of the vehicle. Another type of inflatable vehicle occupant protection device is an inflatable side curtain that inflates away from the vehicle roof to a position between the vehicle occupant and a side structure of the vehicle. Other known types of inflatable vehicle occupant protection devices include seat-mounted side impact air bags, inflatable knee bolsters, and inflatable seat belts. The known inflatable vehicle occupant protection devices are inflated from a deflated condition by inflation fluid provided by an inflator.